Fluid input and diameter measurements in wells



1956 A. D BENNETT ETAL 2,775,121

FLUID INPUT AND DIAMETER MEASUREMENTS IN WELLS.

5 Sheets-Sheet 1 Filed Dec. 29, 1952 HHuoE 0 OE mfiqum O m zom 0 O w m w. I 0 w m N 9 ON vm i Y N 3 III!!! lrl'lllllo L |1| mm m TN '.I Q TmL ww d w m m Q 0 C0O fi ARTHUR o. BENNETT DANIEL SILVERMAN INVENTORS BY W A TTORNE Y Dec. 25, 1956 A. D. BENNETT ETAL 7 FLUID INPUT AND DIAMETER MEASUREMENTS m WELLS Filed Dec. 29, 1952 Y 5 Sheets-Sheet 2 ARTHUR o. BENNETT DANIEL 'SILVERMAN "I H III I1IIIIII|IIIILIU HLdEJO INVENTORS BY W 95 ATTORNEY- Dec. 25, 1956 BENNETT ET AL 2,775,121

FLUID INPUT AND DIAMETER MEASUREMENTS IN WELLS Filed Dec. 29, 1952 V 5 Sheets-Sheet 5 l t I I 8 N i I i l a l 8 I Q 2 .l i! I 1 I IV I A) a I g I l E I 1 l I 1 I l l l l I l l ll l i'i l. v

ARTHUR D. BENNETT DANIEL SILVERMAN INVENTORS W aw ATTORNEY A. D. BENNETT ET AL 2,775,121

Dec. 25, 1956 FLUID INPUT AND DIAMETER MEASUREMENTS IN WELLS 5 Sheets-Sheet 4 Filed Dec.

m 97. 53m J 0 m E 2 I I m Km llll J m m I l Illl I, w 9 0m 76 ARTHUR D. BENNETT DANIEL SILVERMAN A TTORNE Y Dec. 25, 1956 A. D. BENNETT ET AL 2,775,121

FLUID INPUT AND DIAMETER MEASUREMENTS IN WELLS 5 Sheets-Sheet 5 Filed Dec.

INTERFACE VELOCITY MK Wm 11 w CT 4 8/ u \A 3 1. E R @iwmQ m m w H v 3 2 Wm 2M8. M v% m UT J m a u L W 2 .VQ Q\\ m 2? w v HHHHHHHF T R T r m o W M B 5 6 mm W M n 1 a L o E m w v a o mm m mm mm m w W N/ mmomoumm ARTHUR D. BENNETT DANIEL SILVERMAN INVENTORS BY W W- FIG. 12

A TTORNE Y United States Patent FLUID INPUT AND DIAMETER MEASURE- MENTS IN WELLS Arthur D. Bennett and Daniel Silverman, Tulsa, Okla, assignors to Stanolind Oil and Gas Company, Tulsa, Okla., a corporation of Delaware Application December 29, 1952, Serial No. 328,454

5 Claims. (Cl. 73155) This invention relates to fluid-velocity measurements made in well bores and is directed particularly to obtaining data from which both the injection profile of fluids entering the permeable formations of a well and the variations in well-bore cross-sectional area can be determined.

In all types of well measurements involving the velocity of movement of fluids along a well bore, variations in the velocity may occur even though as many variables as possible are being held constant. Thus, in spite of bolding constant both the bottom-hole pressure within a well bore and the total rate of injection of fluids into, or of production of fluids from, the well formations, the fluid velocity as measured at various depths in the well bore may still vary from either or both of two causes. Opposite permeable formations, fluids may enter or leave the well, producing variations in the velocity of fluids moving along the well bore; or the horizontal crosssectional area of the well bore may vary and produce an inverse efiect on the fluid velocity. Any given change of velocity may be due to either one of these two causes separately, or both together, in equal or different degrees. From the character of the velocity change, however, it is generally not possible to determine its cause.

In recognition of these facts, for purposes of correcting fluid-injection or input profiles made in wells utilizing fluid-velocity measurements, measurements of the variations in effective bore-hole cross-sectional area have been separately made, using mechanical calipering instruments. These have often been found inaccurate, however, due to the fact that making mechanical contact at three or four points around the periphery of a well bore does not always reflect the true cross-sectional area of the hole at that level, and also caliper instruments are often not able to respond to the very large and abrupt changes which sometimes occur in the vicinity of soft or alternately hard and soft formations. In addition, it is sometimes impossibleto run a caliper instrument because of the presence of well tubing extending through the portion of well bore of interest. Another common disadvantage is the fact that, in making separate runs with different instruments, discrepancies of depth measurement frequently occur and render difficult or inaccurate the subsequent interpretation or computations.

Injection or input profiles also have frequently been made utilizing fluid interfaces and their movement along a well bore, but the utility of many of these procedures has been limited due to the fact that more than one type of fluid is used, and certain of the injected fluids may adversely aflect the permeability of the formations. Also, the permeability of the formations in relation to certain injected fluids may be different from that in relation to the normally injected fluid.

It is accordingly aprirnary object of our invention to provide a method ofobtaining data from which both the fluid-input profile and the bore-hole cross-sectional area variations can be determined in the same operation.

Another object is to provide a method of determining the true well cross-sectional area variations, regardless of their character, and in the presence of well tubing extending through the section of the well which is of interest. Still another object is to provide a method of measuring the fluid-input profile of a Well using a single type of injection fluid, at substantially the normal rate of injection. A still further object is to provide a method of obtaining data from which the true input profile in the open-hole section of a well bore can be determined, regardless of the nature of the variations in the well-bore cross-sectional area. Other and further objects, uses, and advantages of the invention will become apparent as the description proceeds.

Stated generally, in accordance with our invention, the foregoing and other objects are accomplished by establishing in the fluids in the open hole portion of a well bore one or more interfaces or markers, and then following the movement of said markers or interfaces, while injection of fluids into the well formations and/ or movement of fluids up the well bore into the annular space in the cased portion thereof are taking place. A set of such data is obtained for each of two significantly different fluid-movement conditions. By combining the two sets of data so obtained, a log or profile of fluid input is produced which is substantially independent of borehole area variations; and, conversely, a log of bore-hole area variations is obtained that is independent of the fluidinput properties of the well formations.

The present method therefore amounts to producing two fluid-velocity logs under two conditions of bottom hole pressure and fluid flow such that the measured changes of velocity due to fluid input into the well formations are equal, or can be made so during subsequent calculations. Under these conditions the velocity changes due to bore-hole area variations are not similarly made equal to each other, so that, upon subtraction of the two curves obtained, a resultant log is produced which conveys only the bore-hole area data. This log is then used for correcting and eliminating the area effect in the fluidvelocity log, yielding the input profile by itself.

This will be better understood by reference to the accompanying drawings forming a part of this application and illustrating certain embodiments and modifications of our invention and the manner of interpreting the data obtained. In these drawings,

Figure 1 is a cross-sectional diagrammatic sketch of a well bore, of idealized form for illustrating one embodiment of our invention;

Figures 2 and 3 are resulting and calculated logs of the well of Figure 1;

Figure 4 is a diagrammatic cross-section of a well simi-. lar to Figure l and illustrating an alternative embodiment of our invention;

Figures 5 to 11, inclusive, are resulting recorded or calculated logs of the well of Figure 4 under various conditions, particularly illustrating the interpretation of the data which is obtained;

Figure 12 is a diagrammatic cross-section of a typical well bore showing in some detail most of the testing equipment suitable for use in practicing a preferred embodiment of our invention; and

Figure 13 is a graph showing two representative logs.

obtained in the Well of Figure 12 in carrying out the preferred embodiment of our invention.

Referring now to these drawings in detail and particularly to Figure 1 thereof, a well 20 is. shown diagrammatically in cross-section, in a form which is idealized and simplified to illustrate our invention. Well 20 is equipped With a casing 21 and a tubing 22, the casing 21 being closed at the ground surface by a valve 2 3. Within the annulus 19 between tubing 22 and casing 21 are shown three fluid levels. Level 24 is that to which the annulus liquids drop when all injection of fluids into the well formations has been discontinued, and the well has been allowed to stand a sufficient length of time to come to static equilibrum. Level 25 is that at which the liquids in annulus. 19 stand when fluids are being injected into thewelhformation at a normal or desired rate. The difference in hydrostatic pressure thus represented by the levels 24' and 25*is, therefore, the'increase in bottomhole pressure which occurs when fluids are being injected from the surface through the tubing 22 and thence into the well formationsat the normal rate, assuming that casing valve 23 is open to the atmosphere.

The level 26, between lever 24 and level 25, represents a different liquid level which exists within annulus 19 with valve '23 closed and the upper end of space 19 filled with gas under substantial pressure supplied, for example, by a compressor 27 at the ground suface, while liquids are being injected into the well formations at the normal or desired rate through tubing 22. The difference in levels 25'and-26 therefore represents the equivalent hydrostatic pressure due to the presence of the gas pressure in space 19.

For purposes of explanation it will be assumed that the well bore penetrates five significant formations, 30, 31, 32, 33, and 34. Formations 30, 32, and 34 are assumed to be impermeable and to take no fluid. Formations 31 and 33 are each assumed to have uniformly distributed permeability and to take fluid equally from the well bore. Opposite the impermeable formation 32 the well bore is assumed to be enlarged to twice its normal cross-sectional area.

With gas pressure in the annulus 19 holding level 26 at a stabilized position as shown in the drawing, the well 20 is injected with fresh water through tubing 22 at a constant rate and for a suflicient period of time to create a column of such water filling the well bore at least to the top of permeable formation 31. Injection, still ata constant rate, is then switched to salt water, and as this water emerges from the bottom of tubing 22, it forms a marker or interface 36, with fresh water above and salt water below, which interface rises with varying velocity through the well bore past the various formations. This interface is followedby means well known in the art,.. u,ch as the conductivity electrodes shown in U. S. Patent 2,595,610, for example. Although the interface between thefresh and the salt water is in reality a narrow mixing zone between two miscible liquids ratherthan a visibly sharp boundary between two immiscible liquids suchas oil and water, this. mixing zone remains quite. narrow throughout large distances of travel in the wellannulus. Only a slight vertical movement of the conductivity electrodes awayfrom thecenter of the interface 36 is needed to confirm its sharpness. When the salt water is below the fresh water, the differencein specific gravities no doubt aids in maintaining this sharpness of interface. This is not the complete explanation, however, as interfaces with the salt water above the fresh water have been easily followed for vertical distances of feetormore.

From the resulting data a log is plotted ofthe interface velocity as a function of depth, which log'may take the form of log 40 illustrated in Figure 2. Thedashedline log 41 of Figure 2 represents the same typeof measurement taken with a different input rate through the tubing 22 and into the permeable formations. Otherwise it is exactly like log 40 and may .be used in'the interpretation instead of or in the same way as log 40. To accomplish the purposes of theinvention, however, it is .not necessary to obtain both of logs 40 and 41, as either one alone issuflicient.

After the first velocity traverse of the interface 36 through the formations of interest is completed,-injection is again'switched to fresh water at the previous rate untilthe formations are partly or entirely covered by it. A new interface is then formed by again introducing saltwater through the tubing 22, but this time at an increased rate, over-and above that'during -the first run. In this instance, however, the casing valve 23 is opened slightly and is adjusted to release the gas pressure in annulus 19 at a rate just sufficient to maintain the bottom-hole pressure constant, while fluid level 26, isrising due to the differential increase in salt-water injection rate through tubing 22. That is, the tendency forthe bottom-hole pressure to rise because of the rising liquid level in annulus 19 is exactly offset by the decreasing gas pressure in this space. As before, interface 36 is followed, forv example, by making measurements ofitssuccessive positions, in order: to produce a velocity-depth log like log 42 of Figure 2.

Under these conditions of testing, the bottom-hole pressure does not vary from its value during the first measurements to obtain log 40, with the result that the character and magnitude of the changes in velocity of the interface 36 while passing formations 31-and 33 remain the same as previously. The change in velocity of. the interface 36 as it passes the enlarged portion 32, however, is different. Accordingly, subtracting log 40 from log 42 produces the log 43, shown in Figure 3, whichtherefore represents the velocity log which would be obtained if formations 31 and 33 were taking no fluid, and.the interface were moved up the well due to salt-water injection at a total rate which is exactly equalto the differential increase in rate which was compensated for by release of gas through-valve 23. The velocity log of Figure 3 is thus directly interpretable in terms of variations in the well-bore cross-sectional area, which produce exactly in-v verse proportional variations in interface velocity.

The log of 'Figure 3 can then be utilizedto correct the total interface velocity log40 ofFigure 2 for the efiectof thehole enlargment at formation32. Log 43 showsthat the velocity values of log 40 oppositetheformation32 must be multipliedby two, the factor ofincrease in .well cross-sectional area, to produce the dot-dash curve 44 which, with the solid-line portions of curve 40 opposite formations 30, 31, 33,,and 34, represents the true fluidinput log for well 20, corrected for the bore-hole area variation at the depth of formation 32.

Referring nowto Figure 4, this figure illustratesan alternative,embodimentof the invention. The'well 20,1 the permeable and impermeable formations, and the .hole enlargement are allassurned to be the sameas in Figured. In Figure 4, however, the level 50 represents the fluid level attained in annulus 19 at some intermediate injection rate, less than the full or normal injection rate which produces level 25, instead of, as in Figure 1, representing-a fluid level due to superimposed :gas pressure. 24 here, as in Figure 1, corresponds to the static equilibrium level of annulus fluids for zero injectioninto the formations. v

It is assumed that the water standing. at the static level 24 in annulus 19 'is freshwater. If it :is not, the

salt water in the lower'portion of .well bore20 may ;.be.

forced into the formations by injecting fresh 1 water through tubing 22 for a period-of time andthen allowing static equilibrium'to be reached by discontinuing .the injection. Thereafter injection at a constant rate-is again started through the tubing 22 'using salt water-which forms the interface 36 at the bottom of tubing22 and then movesup annulus 19 as injection continues,-raisiug the level 24.

urements made on the rising interface 36 result.. in ;a velocity log such as 51 shown in Figure .5. Insofar as the rate of injection of fluids into the formations is .small compared to the total injection rate .throughitubing .22,

this log corresponds exactly to 'avolumetri'c .caliperlog ,-f showing'directly'the.effect.of the enlargement at .forma-t tion 32.

The level In the course ofthe injection, it is often preferred to switch the fluid input through the tubing 22 alternately between fresh water and salt water. After a short time this results in a plurality ,of salt water-fresh water interfaces moving up the annulus 19. Successive, rapid surveys through this region show the positions of these interfaces at closely spaced time intervals, so that the com plete velocity data are rapidly obtained. When injection is therefore continued in this manner, intermediate values of the annulus fluid level 50 are obtained, and the successive logs 52, 53, and 54 result as the formations 31 and 33 take fluids at various increasing rates.

Each of these separate logs, like the log 51, is accurate only to the extent thatthe injection rate may be assumed constant during the time of obtaining the data for any one log. This is approximaely true if the bottomhole pressure variation required to change the injection rate by a substantial amount is also substantial. The dashed line 55 on the right of Figure 6 represents the rate of rise of an interface due to the injection through tubing 22, assuming no input into the well formations and no variations in the well diameter. For purposes of this description, this line may therefore be termed the injection-rate line or the injection-rate velocity.

As the injection at constant rate is continued, operating level is finally approached, and the interfacevelocity log obtained from the resulting data is shown as log 56 in Figure 7.

Assuming now that there are available at least two of the curves 52, 53, and 54, which are obtained under different conditions of fluid injection into the formations 31 and 33 and correspondingly different fractions of the fluid traveling up annulus 19, these two curves are now utilized to compute a well-caliper curve and corrected fluid-input curve or profile.

In Figure 8 are two of such curves, curves 60 and 61, which are representative of those which would be obtained in a well with slightly different conditions assumed as to the amount of enlargement at the formation 32. For properly illustrating this interpretation, therefore, let it be assumed that the area of the well bore at formation 32 is three times that at other places. It will be observed on curves 60 and 61 that this three-times enlargement reduces the interface velocity to one-third of the value which it would otherwise have in the open-hole portions of the well. In this figure the injection-rate line 55 is taken as corresponding to an arbitrary number of velocity units, such as eighteen.

For the purposes of this interpretation it is preferred to transfer these units onto a reverse scale, which may be designated the Q: scale, as it represents in genera-l terms the quantity of the injected fluid which enters the formations 31 and 33. The Q: scale corresponds to the foregoing velocity scale in size of units, except that the Q: value of zero now coincides with the injection-rate velocity line 55 of the velocity scale.

Figure 9 shows the same two curves 60 and 61 plotted to the new Q: scale. The interpretation here consists in multiplying each value of abscissa of the curve 60 by a factor to make it coincide with the curve 61 in the formation 3%, or at any similar place where the bore hole is of known or normal size and no injection of fluids into the formation is taking place. This might be within annular space 19 above the bottom of casing 21. For these curves, this multiplying factor is seen to be 10/6 or 1.67. Upon multiplying each point of curve 60 by this factor and replotting the result on the same Qt scale, the graphs shown in Figure 10 are obtained Where solid curve 60 corresponds to the former curve 60 multiplied by the factor 1.67. The difference between curve 60 and curve 61, which is plotted as the dot-dash curve 63 of Figure 11, represents the log of bore-hole area to the Q: scale.

In order to obtain a quantitative hole-size log it is necessary to multiply the abscissas of this log by a correction factor. This is equal to the Q! value in the formation for the smaller of the velocity logs, 60, divided by the difference between the Q1 values (in formation 30) of the two logs 60 and 61. In this case, it is (l06) Multiplying the abscissas of dot-dash curve 63 of Figure ll by this factor of 1.5 gives the solid-line curve 64, which is the correct caliper or area-variation log, when referred to the velocity scale superimposed at the top of this figure. This is the same velocity scale as was previously used in the initial plotting of the logs, zero velocity corresponding to a Q: of eighteen units. Curve 64 may be used directly in the interpretation of the fluidinput curve of either of logs 60 or 61 to eliminate the effects of variations in bore-hole cross-sectional area.

Referring again to Figure 8, multiplication of the abscissas of curve 60 opposite formation 32 by the correction factor of three, which is the inverse of the velocity-scale reading of curve 64, produces the dotdash line 65 opposite formation 32 which, along with the solid-line portions of this curve in the formations 30, 31, 33, and 34, forms the correct fluid-input profile, in terms of the velocity variations produced by fluid entering the formations, free from the effects of varying borehole size.

In Figure 12 is shown a well in cross-section, with the apparatus set-up necessary to carry out a preferred embodiment of our invention. This arrangement of appar atus takes care of the fact that some wells require injection with surface pressure, so that the annulus 19 cannot be left open for carrying out the manipulations of the foregoing embodiment. This Figure 12 embodiment further provides for making the fluid-input profile measurements at substantially the input rate that it is desired to use in normal injection practice.

This last is a matter of considerable importance, because a number of wells have been found which show anomalous variations in the fluid-input profile, dependent upon the rate of fluid injection. Also, wells have been found where a considerable period of time is required for dynamic equilibrium to be reached following a change in the total rate of liquid injection. In these wells it is generally noticed that, when the injection rate is increased to a higher total value, the increase of surface pressure necessary for the higher injection rate does not build up immediately but takes a substantial period of time to approach the new higher stabilized value.

In this embodiment the well 70 is prepared for testing by replacing the usual casing head with an offset casing head 72. having a stufiing box 73 through which the electrical logging cable 74 may pass carrying the detecting electrodes 75. At the well head, logging cable 74 passes over a sheave 76 to a reel 77 from which an electrical connection 78 is made to a recorder 79. The well tubing 22 is set with its outlet as near as possible to the bottom of well 70, and in any event below the permeable zone 71 of this well.

It will be understood that a similar casing-head arrangement will ordinarily be used during the time that gas under pressure is maintained in space 19 in carrying out the embodiment illustrated by Figure 1.

Connected to the top of tubing 22 througha valve SE, a meter 82, and a pump 83, is a supply vessel 84 containing a liquid contrasting with that normally introduced into the well, which liquid may be fresh water in the event salt water is the normal injection liquid. A pressure gauge 86 on tubing 22 registers the injection pressure applied at the ground surface. Also connected to tubing 22 through a valve 88, a meter 89, and a control valve W is the normal supply 91 of injected liquid such as brine or salt water. Connected to the casing annulus 19 by a pipe 93, through a valve 94 and meter 95, is a receiving tank 96 in which may be stored the liquid flowing casing annulus19, designated by'the letter Qc. appearsin Figure 12, the quantity of theinjected liquidgente'ring permeable'zone 71 is designated by'the letter Qr, while that injected through the tubing 22is designated as Qt. This means that at all times the re lation holds that After the well equipment is thus prepared for the test, therliquid' levels in the casing annulus 19 and tubing 22 will normally be below the ground level, depending upon the-characteristics of permeable zone '7 injection of the normally'injectedliquid from source 91, which is tobe understood as'including the pumping equipment normally used for injecting with surface pressure, for exampleisalt' water, is-then begun at any convenient rate untilannulus 19 is filled'to casing head 72. During this time 'the valves 83, 90 and 94 are opened, and valve St is closed. Air in annulus 19 escapes through valve 94 and is-vented to the atmosphere through tank 96. the air in annulus 19 is displaced, and liquid begins to buildup in tank 96, the rate of salt water injection is adjusted, by means of valve 88 and observation of meter 89, to a value at or slightly below the normal injection rate for well 70. The bottom-hole pressure When then subsequently attains a constant value, determined by the fluid head and the small pressure drop due to the frictionof fluidfiow in annulus 19 and the piping to tank 96.

Atthis time the volumetric fiow rates are given by the foregoing equation Qt=Qf+Qc where the injection rates have the same meaning as above. During and immediately after the period when the bottom-hole pressure is increasing, that is, during the filling of the casing annulus 19, the intake rate Qr into the formations is greater than normal. When the fluid level in the casing first reaches the ground surface, Qr is therefore greater than the stabilized or equilibrium value associated with the newly-attained bottom-hole pressure; and similarly, for the fixed injection rate Qt, the casing flow rate QC is less than normal. During the ensuing period of stabilization of the various flows, Qi; is maintained constant by observingxrneter fifi'and readjusting valve 3? as necessary. Q0 is monitored by observing meter 95 and will be foundto increase to aconstant value, while Qr is correspondingly decreasing to a steady-state value at the bottom of well 70, which value is the normal Qr for the existing constant bottom-hole pressure. Pressure gauge 86 at thistime indicatesslightly more than zero gauge pressure.

Testing is then begun by switching for a brief time from injection ofsalt water to injection of fresh water and then returning to salt water injection, keeping the total injection rate Qt into the tubing constant at all times.- This switching is preferably performed by closing valve:88 and simultaneously opening valve 81, regulating the speed of pump 83 by'observation of meter 82, and adjusting valve 81 as necessary, so that the same volumetric rate of water injection from tank 84 is'provided as the salt-waterinjection rate previously registered by 1neter 89. Following a short period of'injection of'fresh waterfrorn supply 84, the supply is again switched by closing valve 81 and opening valve 88 and resuming saltwater injection from source 9.1. When thissalt water reaches thebottom of tubing 22 and passes out into annulus'19 ofwell 70, it forms an interface with the previously injected body of' fresh water, and this interface 36 is followed by the electrode device 75, as motion upwardly through the permeable zone 71 takes place. From the resultingdata the velocity of movement of this interface 36'is plotted to yield the curve 101 of Figure 13.

Atsecond test is now carried out under the exact conditions .of'bottom hole 'pressure which exist during injection -at :th'e' rate which is normal for the 1 formation 71; Valve :94 is clos'ed "sozthat there is no further flow up the annulus 1'9 into'tank 96. A conditionat'the bottom of well-* therefore exists such that Qt and Q1 a're equall Qt will initially tend to decrease, as the formations must take all of the water that is injected. When'this occurs,' it is broughtback' to its correct value by adju'smen'tof valve 88 and application of such additional surface pressure as is necessary.

In manywellsitisfound' that the tubing pressure read on gauge '86 required to maintain Qt' at the full or normal value is initially less than the pressure assumed later, after a period of stabilization. This is because the formation 71 offers less'resistance to input flow immediately after the increase of bottom-hole pressure than it does after a p'eriod'of stabilization at the higher rate. As the injection is' continued, the pressure to maintain Qt constant increases gradually, requiring that valve 83 be progressively opened, or that more pressure from the source 9i be provided. As the formation input to 71 stabilizes, the bottom-hole pressure and the tubing pressure indicated by gauge 86 finally assume constant values that are typical of the normal well operation.

At this time a newinterface for observation and testing is created by again switching the injection temporarily from the salt waterof supply 91 to the fresh water of supply 81 in the samemanner as previously, at the same time maintaining Qt as nearly constant as possible. Upon subsequently switching back to salt water from supply 91, the desired interface 36 is formed at the bottom of tubing 22 and is followed upwardly through the formation 71,

' providing data which may be plotted as the velocity log 102 of Figure 13. Since these data are taken under stabilized conditions of the normal bottom-hole pressure and injection rate for this well, curve 102 will, except for the effect of variations in the bore-hole cross-sectional area, be the normal input profile of the well 70.

The data on these two curves of'interface velocity as a function of depth are then utilized to yield the logo)? the caliper variations and the fluid-input profile in exactly the same manner as was described in connection with Figure 8.

As was mentioned in connection with the previous embodiments, a plurality of interfaces or markers can be createdby alternately switching the injection fluid back and forth between fresh Water and salt water. The data from which the velocity logs are prepared are then rapidly obtained by traversing the electrodes repeatedly up and down through the'test section of the weil, thus locating the position occupied by each interface after each short, known interval of time.

While our invention has been described with reference to the foregoing specific embodiments and modifications thereof, it is to be understood that these are for purposes of illustration only and that still further embodiments and modifications will be apparent to those skilled in the art. The scope of our-invention, therefore, should not be considered as limited to the details thus set forth but should properly be ascertained from the scope of the appendedclaims.

We claim:

1. A method of obtaining data from which both the fluid-injection profile and the holesize variations of a well bore can be determined comprising, in combination, the steps of injecting liquid into a well through a tubing extending to a level below the permeable formations of said well, saidliquidtraveling upwardly outside said'tubing into said formationsand into the annulus outside said tubing above said formations under such'conditions that the ratio of the flow up said annulus to the flow entering said formations has one value, establishing a detectable marker in the fluid stream emerging from said tubing, following and recording the motion of said marker'past said permeable formations, altering the conditions of injection' to change said ratio of flows to a second value,

establishingl a second detectable marker in said fluid stream, and following and recording the motion of said second marker, whereby two logs of the velocity of said markers may be plotted, from which logs said profile and hole-size variations may be computed independently of each other.

2. A method of obtaining data from which both the fluid-injection profile and the hole-size variations of a well bore can be determined comprising, in combination, the steps of building up a substantial gas pressure in the annular space of said well bore outside a well tubing therein, injecting fluid into said well bore through said well tubing to a level below the exposed permeable formations at a first rate such that all of said fluid enters said formations, said gas pressure substantially preventing any fluid movement up said annular space above said formations, establishing a detectable marker in the fluid stream emerging from said tubing, following and recording the motion of said marker past said permeable formations, increasing the injection rate through said tubing while simultaneously releasing said gas pressure at a rate to maintain a substantially constant bottom-hole pressure in said well, establishing a second marker in said fluid stream, and following and recording the motion of said second marker, whereby two logs of the velocity of said markers may be plotted, from which logs said profile and hole-size variations may be computed independently of each other.

3. A method of obtaining data from which the fluidinjection profile and the hole-size variations of a well bore can be determined comprising, in combination, the steps of injecting liquid through a tubing extending to a point below the exposed permeable formations of a well at a constant rate which is approximately the normal injection rate for said Well, the annular space outside said tubing being open at the surface so that part of said liquid enters the well formations and part flows up said annular space, continuing said injection until the ratio of flows into the formations and up said annular space to the surface reaches a substantially constant value, establishing a detectable marker in the fluid stream emerging from said tubing, following and recording the motion of said marker past the permeable formations, closing said annular space at the surface to stop substantially all of the flow up said annular space while maintaining the injection through said tubing at said normal rate, whereby substantially all of said injected liquid is directed into the formation, holding said tubing injection rate constant until the surface injection pressure attains a stable value, establishing a second marker in said fluid stream as it emerges from said tubing, and following and recording the motion of said second marker past said permeable formations, whereby two logs of the velocity of said markers may be plotted from which said profile and holesize variations may be computed independently of each other.

10 4. A method of obtaining data from which both the fluid-injection profile and the hole-size variations of a well bore can be determined comprising, in combination, the steps of injecting liquid into a well through a tubing extending to a level below the permeable formations of said well, said liquid traveling upwardly outside said tubing into said formations and into the annulus outside said tubing above said formations under such conditions that the ratio of flow up said annulus to the flow entering said formations has one value, alternating the injected liquid between salt water and fresh Water to produce a plurality of spaced detectable interfaces in said upwardly traveling liquid, repeatedly scanning said upwardly traveling liquid to locate the depths of each of said intenfaces at successive known intervals of time, altering the conditions of injection to change said ratio of flows to a second value, producing a second plurality of detectable interfaces in said upwardly traveling liquid, and repeatedly scanning said upwardlytraveling liquid to locate the depths of each of said second plurality of interfaces at successive known intervals of time, whereby two logs of the velocity of movement of said fluids through said Well bore may be plotted, from which logs said profile and hole-size variations may be computed independently of each other.

5. A method of obtaining data from which both the fluid-injection profile and the hole-size variations of a well bore can be determined comprising, in combination, the steps of establishing a marker in the fluid column outside a tubing extending to a level below the permeable formations of said well with the fluids in said well bore being substantially at static equilibrium, initiating injection of liquid through said tubing into said well, following and recording the motion of said marker upwardly through the well bore outside said tubing before the portion of injected liquid entering said formation becomes substantial, continuing the introduction of liquid through said tubing until a substantial portion is entering said formations, establishing a second marker in the fluid stream emerging from said tubing, and following and recording the motion of said second marker past said permeable formations, whereby two logs of the velocity of said markers may be plotted, the first being substantially a log of the velocity elfects of hole-size variations which may be use to correct the second log to obtain a true fluid-injection profile.

References Cited in the file of this patent UNITED STATES PATENTS 

